A possible reason why fluorescent lamps fail is diminished emitting power on the part of the electrodes (what is called the end-of-life effect). Said effect occurs at the end of a fluorescent lamp's useful life in one of the two electrodes. The result is that the discharge current flows through the lamp more readily in one direction than in the opposite direction. The fluorescent lamp functions in that case as a rectifier. The electrode that is unable to emit therein becomes so hot that high temperatures can occur on the lamp's surface. In an extreme case, the glass bulb of small-diameter fluorescent lamps can melt.
An electronic ballast (EB) for actuating the fluorescent lamp must promptly detect said one such fault incident and either limit the output current and output voltage in each case to a non-critical value or switch the fluorescent lamp off.
The EB has to perform various control and monitoring functions beyond actually operating the lamp. Depending in particular on how the EB is connected, control and monitoring functions of such kind require separate circuitry components.